The present invention relates to a parasitic microorganism being able to kill dinoflagellates, a method for eliminating or suppressing growth and/or replication of harmful dinoflagellates of, e.g., the genuses Dinophysis, and Alexandrium, method for propagating said microorgansm, and a composition containing said microorganism for carrying out said method.
The object of the present invention is to obtain a possibility of eliminating poisonous or otherwise harmful dinoflagellates from the sea, thereby avoiding accumulation of dinoflagellate related toxins in shellfish, such as mussels and oysters.
Most coastal waters are even so often invaded by harmful microalgae blooms. Certain toxic algae will kill wild and farmed fish, and particularly the latter suffers, as it can not escape from the algae in contrast to the wild ones. This will cause an immediate economical impact on the breeders of farmed fish, as all stages of the farmed fish will be killed, and several years production will be affected. Other algae produce potent toxins that accumulate in filter-feeding shellfish and poison human consumers. Thus marketing and sale of such shellfish from such affected coastal areas is forbidden for long periods.
Bloom of microalgae is further harmful as the algae when dead will consume most of the oxygen present in the water, thereby causing bottom fauna death, and/or fish flight.
Toxic marine dinoflagellates can cause shellfish, e.g. mussels and oysters, to accumulate toxins in such concentrations that they become dangerous as human food. Toxic dinoflagellates can cause different types of shellfish poisoning; DSP (Diarrhetic Shellfish Poisoning, caused by members of the genuses Dinophysis and Prorocentrum), PSP (Paralytic Shellfish Poisoning, caused by the genuses Alexandrium, Gymnodinium, and Pyrodinium) and NSP (Neurotoxic Shellfish Poisoning, caused by the genus Gymnodinium breve). Those intoxifications of the mussels inhibits the mussel industry as the mussels can not be harvested for shorter or longer periods. This production loss of the shellfish industry is estimated to 1-2 billions USD yearly. A further very important aspect is also that those who harvest shellfish for food consumption, have no possibility to check for high toxin content in the mussels. The shellfish industry has grown much during the last decades and is expected to grow even more due to the need of food for a growing human population. The aqua culture and shellfish market is expanding but is also suffering from marine pests, such as toxic marine phytoplankton.
A marine microalgae bloom is widely defined when the water is discoloured and/or comprises a cell concentration of 1xc3x97106 cells per liter. The recording of those blooms is ancient but it is only in modern time we have been aware of the problems and suffer to a larger extent therefrom. It is also suspected that human eutrofication is causing the more intense and more frequently occurring blooms. The algae species that are producing toxins and are capable of forming blooms are mostly belonging to the dinoflagellate group of organisms.
In some Spanish fjords mussel harvesting sites have been closed down up to a half year. This could, hopefully be shortened down to some weeks, if a regulatory parasite to the toxic dinoflagellates is found.
Thus scientists are struggling to find methods to control those harmful microalgae blooms and are intensifying the efforts to find such methods (D. A. Anderson, Nature, 388:513-514, August, 1997).
At present the best method is to spread huge amounts of clay into the water in order to clog the phytoplankton and hence rapidly precipitating them out of the water column (corresponding to the flocculation method in industrial sewage and waste water treatment). This is, however, a very costly method and labour intensive. The method has only been applied in the republic of China (D. A. Anderson, Nature, 388:513-514, August, 1997).
JP patent specification 6001701 discloses red tide controlling material comprising a fibrous material carrier supporting a highly unsaturated fatty acid, whereby the material is supposed to kill the red tide plankton in contact therewith.
JP patent specification 5169088 discloses use of an attack bacteria of red tide plankton inhibitor comprising bentonite or kaolin-based clay-like particles.
JP patent specification 6016504 discloses a surfactant composition for controlling red tide, which surfactant composition comprises polyoxyalkylene alkyl ether, polyalkylene glycol fatty acid ester, polyoxyalkylene fatty acid amide, and polyoxyalkylene alkyl amine, which composition is sprayed onto the red tide plankton.
JP patent specification 8289693 discloses the use of radioactive compounds for killing red tide plankton.
F. J. R. Taylor, J. Fish. Res. Bd. Canada, 25(10):2241-2245 (1968) discusses the parasitism of toxin-producing dinoflagellate Gonyaulax catenella by the endoparasitic dinoflagellate Amoebophyra ceratii, and concludes that it seems possible that the answer to harmful plankton blooms is the use of a biological control agent, similar to A. ceratii, as A. ceratti was not totally fatal to the host population in the case investigated.
Elbrxc3xa4cher, M. et al, in xe2x80x9cPhysiological Ecology of Harmful Algal Bloomsxe2x80x9d, D. M. Anderson, A. D. Cembella and G. M. Hallegraeff, eds. Springer-Verlag Berlin Heidelberg, pp 351-363 (1998) discuss parasites of harmful algae as a tool for preventing harmful microalgael blooms. In this article the use of A. ceratii as proposed by Taylor, supra, seems to have been dismissed by Nishitani, L. et al, in xe2x80x9cToxic Dinoflagellatesxe2x80x9d, D. M. Anderson et al, eds, Elsevier Sci. Publ. Co. New York, N.Y. pp 225-230 (1985).
Coats, D. W. et al., Aquat. Microb. Ecol., 11:1-9, (1996) discuss parasitism of photosynthetic dinoflagellates in a shallow subestuary of Chesapeake Bay, USA. I. a. Coats et al discuss the parasitism of A. ceratii on Alexandrium (=Gonyaulax) catenella according to Taylor, supra, and the dismissal of Nishitani et al, supra, and are of the opinion that the Taylor""s suggestion should be reexamined.
Scientists have been searching for a natural method of controlling these blooms and the use of some kind of parasitic organism or predator has been in mind and requested since parasites have been found to be an important regulating factor of a microalgae bloom. (Coats et al, supra). However, until today no such organism has been found that sucessfully is inhibiting a toxic, or otherwise harmful bloom, or could be industrially multiplied into an effective bloom inhibitor.
One parasite known to infect the toxic dinoflagellate genus Dinophysis is the parasitic dinoflagellate Amoebophrya ceratii (Taylor et al, supra). It is able to infect Dinophysis but is not able to graze down a bloom of the same species. (Coats et al, supra). This parasite has neither been actively used in attempts to control a dinoflagellate bloom, i.e. it has not been artificially cultured and reinserted in the natural environment as a pest controlling agent.
Thus the only in vivo method today, for terminating marine microalgae blooms is to put large amounts of clay into the sea to obtain a flocculation and precipitation of the algae. An intense research for biological controllers of the marine algae blooms is ongoing but today no such organism is known to work efficiently or is available to give an efficient control of the blooms. (Elbrxc3xa4cher et al, supra). The parasitic dinoflagellate Amoebophrya ceratii is able to infect Dinophysis sp. but is not able to control a bloom of the same species. Amoebophrya ceratii has neither been used to actively control a bloom of dinoflagellates.